Method of and means for controlling electric motors



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No. 599,804. Patented Mar. 1, 1898.

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Patented Mar. 1,-1898.

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S.H .SHORT. METHOD OF AND MEANS FOR CONTROLLING ELECTRIC MOTORS. No. 599,804. Patented Mar. 1,1898.

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SIDNEY H. SHORT, OF CLEVELAND, OIIIO.

METHOD OF AND MEANS FOR CONTROLLING ELECTRIC MOTORS.

SPECIFICATION forming part of Letters Patent No. 599,804, dated March 1, 1898.

Application filed May 19, 1897- SEIiE-I NO. 687,212: (N0 model.)

To (0Z5 w/wm it may concern.-

Be it known that I, SIDNEY H. SHORT, a citizen of the United States,residin g at Cleveland, in the county of Ouyahoga and State of Ohio, have invented a new and useful Method of and Means for Controlling Electric Motors, of which the following is a specification.

This invention relates to methods of and means for controlling electric motors.

The object of the invention is to provide an apparatus and mode of operation for controlling electric motors for traction purposes in a manner to secure a rapid acceleration of the car or train and with a much less consumption of power in starting the train and in maintaining the proper speed.

A further object of the invention is to provide an arrangement and method of control for motors particularly adapted for use on trains which are started and stopped oftenas, for instance, in elevated-railway service and in interurban and suburban trains.

Further objects of the invention will appear more fully hereinafter.

The invention consists, substantially,in the construction, combination, arrangement, location, and mode of procedure, all as will more fully hereinafter appear, as shown in the accompanying drawings, and finally specifieally pointed out in the appended claims.

Referring to the drawings and to the various views and reference signs appearing there on, Figure 1 is a view in diagram illustrating the arrangement of circuits and the circuitcontrolling contacts for carrying the principles of my invention into operation. Fig. 2 is a diagram illustrating the leads of the circuits under varying positions of the controller. Fig. 8 is a view similar to Fig. 1, wherein a less amount of resistance is employed. at illustrates in diagram the various circuits and the changes therein under the several steps in the operation of the controller shown in Fig. Fig. 5 is a View similar to Figs. 1 and 3 of an arrangement employing two or more motors and embodying the principles of my invention and the method of coupling up the motors in accordance with my invention, in series or in parallel, to produce the effect of a uniform acceleration. Fig. 6 illustrates, diagrammatically, the various changes in the circuits resulting from the various positions of the apparatus shown in Fig. 5. Fig. 7 is a diagram illustrating the acceleration-curve of an ordinary series motor. Fig. 8 is a diagram illustrating the acceleration-curve of a motor operated in accordance with the principles of control embodying my invention. Fig. 9 is a diagram illustrating a theoretical power-curve.

In the practical operation of motors for traction purposes it is exceedingly desirable to maintain a constant acceleration of the train until the desired speed is attained and thereafter for the train to proceed at a uniform speed. Such a desirable result cannot be obtained under prior methods of control for reasons which I shall endeavor now to explain.

In the case of an ordinary series motor for instance, such as is usually employed for traction purposesin order to start the train a large current is turned onto the motor to start it, thereby developing in the motor a very large horizontal effort. For the first few seconds the acceleration of the motor, and hence of the train, would be rapid and satisfactory. If this acceleration would continue to be uniform, a theoretically ideal condition would be attained, and the acceleration-curve of the motor would be indicated by a straight line A, Fig. 7, and such uniform acceleration in speed would accomplish a starting of the train from rest in a satisfactory, quick, and speedy manner, and would therefore effect a large saving of time in getting under way. If this uniform acceleration were to continue, however, the train would reach a rate of speed far beyond the safety limit; but in the case of an ordinary series motor, however, as the armature of the motor gets under headway a counter electromotive force is set up therein, which reduces the current flowing through the motor. This reduction of current flowing through the motor results in a falling off of the horizontal effort, with a corresponding falling off of the increase in speed per second each second, so that instead of the ideal acceleration of the curve A of Fig. 7 such curve takes the form of that shown at B, Fig. 7, until finally the current falls to a point where it will develop only the power necessary to move the train at a uniform speed. This variation of the curve B from the straight or theoretically ideal acceleration-curve A illustrates a 2 59.9,soe

fall in the acceleration of the motor and train, and hence a departure from the most satisfactory and economical operation. of the motor.

It is the purpose of my invention to provide amethod of control wherein the acceleration in speed is uniform, or practically so, until the required speed is attained, and from that point onward the acceleration is arrested and a uniform speed is maintained, thus resulting in an acceleration-curve C, Fig. 8, substantially the. same as the theoretically perfect curve A of Fig. 7, such uniform acceleration resulting in the train increasing its speed a given number of feet per second for each second it is in operation. If this uniform acceleration were to continue, as above described, a too high or rapid speed would be developed, and therefore my method of control contemplates arresting the acceleration when the desired speed is attained and thereafter permitting the train to continue to run at a uniform speed. Thus it will be seen that in a method of control embodying these principles the train will rapidly and quickly attain its desired speed in a shorter space of time than heretofore and with a much less consumption of power, and hence saving time in driving the train from one station to another, the train, getting under headway rapidly and quickly under a uniform acceleration of speed until the desired speed is attained, when the acceleration is arrested, and a uniform speed thereafter is maintained until it is again desired to stop the train.

Referring to Fig. 1, illustrating an embodiment of the principles above outlined, reference sign M designates a motor; T, the trolley-circuit therefor; F, F, F and F the fieldmagnet coils; R, R R R and R resistances; 1, 2, 3, 4, 5, 6, 7, 8, and 9, suitable contacts, and D and E portions of cooperating contacts,which may comprise conducting-segmets 1, 2 3, 45, 5 6*, 7 8, and 9, the several points 1 2 3 1, &c., and the corresponding conducting-strips 1 2 3 800., being relatively movable, so as to be moved into or out of contact with each other. In the particular form shown the strips 1 2 3', &c., are mounted upon the surface of the controller-cylinder, the diagram Fig. 1 illustrating such surface developed. The portion D of the controllercylinder is insulated from the portion E, as indicated at X X, Fig. 1.

The motor M is provided with a very large field-magnet in which the iron is not thoroughly saturated with lines of magnetic force under ordinary conditions under which it is expected to operated, so that any variation in the number of ampere-turns on the magnetcore will greatly influence the speed of the armature. It is therefore necessary in accordance with the principles of my improved method of control that the reluctance of the magnetic circuit of the motors employed in connection therewith should be moderately low and that the windings of the field-mag nets be varied considerably without resulting in undue sparking at the commutators under great Variations of load. In other words, the motor should be of larger capacity than is ordinarily used at present for the same class of work.

The first operation of a controller embodying myinvention is for the motorman to move the controller-cylinder D E into the position indicated by dotted lines at A, Fig. 1. The motor-circuit will thereupon be made as follows: from the trolley T, through the windings of the motor-field magnet, the motor M, resistances B B R B B, strip 3, and thence to strip 9, the several strips 3, A", 5, 6, 7 8, and 9 being in electrical connection with each other, from strip 9 to contact 9, thence through the automatic arrangement for automatically actuating the controller-cylinder. This automatic arrangement may comprise a ratchet G, suitably mounted on the controllercylinder, in the teeth of which is arranged to engage a lever H. A suitable automaticallyoperated motor, preferably included in the circuit above described, is arranged to operate the pawl arm or lever H. Many different arrangements of motor and specific constructions thereof may be employed for this purpose.

While I have shown and will now describe a particular form and arrangement of apparatus for accomplishing the desired result, I desire it to be understood that I do not limit or confine myself thereto, as the principles thereof may be embodied in a wide variety of specific forms and arrangement of apparatus and still fall within the spirit and scope of my invention. In the particular form shown the pawl-lever H is pivotally connected to one end of a rock-lever l, to the other end I of which lever is connected a magnetic core J, arranged to form the core of the solenoid K, the coils of which solenoid are included in the circuit connection afrom contact 9. Suitable means for cutting the coils of solenoid K into and out of live circuit with contact 9 automatically may be provided. This may be accomplished in any suitable and convenient manner, and while I have shown and will now describe a suitable and convenient arrangement for accomplishing the desired object I do not desire to be limited or restricted thereto, the arrangement shown being merely illustrative of an operative apparatus for accomplishing the desired result. In the form shown the circuit connection a, after passing through the coils of solenoid K, includes a connection Z) and the coils of a magnet Q, and thence through connection g to ground. A lever N, carrying the armature of the magnet Q, is arranged to be attracted when said magnet is energized, and when so attracted said armature-lever N makes contact with a stop 0, included in a branch connection a from connection to, thereby completing the circuit from contact 9, through connections a and 0, contact 0, lever N, connection I), coils of magnet Q, and connection 9 to ground.

A spring P is arranged to normally maintain the lever N against a stop S and out of contact with the contact 0. From this arrangement it will be seen that when the controllercylinder is turned by the motorman into position indicated by dotted line A, Fig. 1, the

circuit through the motor and all the resistances is completed, as above described, to contact 9, thence through connection a, the mo tor K, connection I), the coils Q, and connection g to ground. As soon as current begins to flow through the windings of motor K the core J is drawn into said coils, thereby rocking rock-lever 1 against the action of spring L and in a direction to move the pawl-lever H in the direction indicated by arrow, Fig. 1, and marked On. This movement of pawllever H, however, does not effect a movement of the controller-cylinder, because there is no tooth of ratchet G in advance of the arm of pawl-lever H. The current passing from motor K through magnet Q effects an attraction of the armature-lever N, thereby establishin g contact between said armaturelever and the contact 0, thereupon completing the short circuit through connection 0, contact O, armature-lever N, connection I), the windings of Q, and connection g to ground, thus short-circuiting the motor K and hence allowing spring L to rock lever I in the opposite direction to that above described and causing the end of pawl-lever H to engage behind the first tooth of ratchetG. Under this condition the motor begins to accelerate. As the motor starts up the counter electromotive force above referred to begins to develop in the motor, which, if permitted to continue, would cause a falling off of the acceleration, and hence the production of the accelerationcurve B, as indicated in diagram in Fig. 7. The development of this counter electromotive force in the motor causes a reduction in the current traversing the relay The tension of spring P is so regulated that when the current falls to below a certain point the retractile P comes into operation to separate the armature-lever N from contact 0, thereby breaking the short circuit described above and reestablishing the circuit through motor K. The reestablishment of the circuit through the auxiliary motor K effects a forward projection of pawl-lever H, which, through the engagement of the front end thereof with the first tooth of ratchet G, effects a movement of the controllencylinder in a direction to cause contact-stri p r to make contact with the point 4. The current through the motor now passes only through the resistances R E R the resistance R ein short-circuited by the corn tact established between point r and strip 4P. The cutting out of this resistance R has the effect of again increasing the current through the motor, so as to maintain a constant acceleration. At thesame time the increase in the current due to cutting out resistance R again causes the relay Q, to operate to again shortcircuit the auxiliary motor K automatically until the current through the motor again falls below the desired point by reason of the continued development of the counter electromotive force therein until the relay is again opened by such fall of current and the auxiliary motor K is again out into live circuit, thereby advancing the ratchet G another step, thus bringing contact 5 and strip 5 into electrical connection, and hence short-circuiting resistance R thus again increasing the current through the motor-circuit, again actuating auxiliary motor K and advancing the controller another step in the manner above described, and so on, thus maintaining a constant 0r practically constant acceleration of the motor until finally, by the strip 8 contacting with the point 8, all the resistances are cut out of the motor-circuit. In the meantime, and when the controller is moved to its first position A, as above explained, the c011- tact-strips 1 and 2 are brought into contact with the points 1 and 2, respectively,the strips 1 and 2 being in electrical connection with each other. The points 1 and 2 respectively form the terminals of the coils F F of the motor-field magnet, and hence so long as strips 1 and 2" remain in contact with the points 1 and 2 the coils F F are short-circuited out of the field-magnet circuit, and hence during the conditions above described,wherein the resistances R R B &c., are successively cut out of the motorcircnit, said coils F F of the field-magnet windings remain short-circuited, leaving only the coils F F, 850., to produce the lines of magnetic force in the armature of the motor. hen finally the controller-cylinder arrives, under the automatic action thereof above described, in the position indicated by dotted line B, Fig. 1, the current during the several steps mentioned remaining fairly constant, slightly rising above the normal accelerating-current as the resistances are successively cut out, and dropping below the normal acceleratingcurrent, slightly, as the counter electromotive force develops. If left in this position, the motor would thereafter rapidly develop a speed greater than that required. The parts are so constructed and arranged, however, that when the point indicated by dotted line B is reached the desired speed has been at tained, and therefore by suitably constructing and arranging the teeth of ratchet G the automatic action of the controller ceases at this point, but during all the preceding operations and up to this position of the parts a large por' tion of the field of the motor has been shortcircuited and out of use, as above described. Now in order to arrest the acceleration of the motor, the desired speed having been attained, so as to permit the motor to continue to operate at a constant speed, the motorman now turns, by means of the controller-handle or otherwise, the controller-cylinder from the position indicated by dotted line B to that indicated by the line C, Fig. 1. This movement of the controller, effected by the motorman, manually or otherwise, but under control of the motorman, breaks the short circuit of coils F F of the motor-field by breaking contact between the strips 1 and 2 and their cooperating contacts 1 and 2, thus causing the motor-current from the trolley T to traverse all the windings of the motor-field, and hence more magnetic lines are forced through the armature of motor M, thus cutting down the motor-current by building up the counter electromotive force of the armature to a point which is just sufficient to maintain the motor, and hence the train, at a uniform speed thereafter. This movement by the motorman of the controller to the position indicated by line C does not affect the resistance-circuits, the motor continuing to operate with the increased number of ampere-turns around the core of the fieldmagnet to point 8 without any resistance, thence to strip 8, strip 9, contact 9, and thence on, as above described, either through the short circuit 0, O, N, b, and g to ground or else through connection a, K, I), Q, and g to ground, it being understood that at this point the automatic action of the controller-cylinder has ceased, and hence it is immaterial which of the above-described circuits from point 9 on the current may take. Under this condition the motor has attained through the constant acceleration described its desired speed, and then the acceleration has been arrested, and the motor continues to operate at a uniform speed thereafter.

From the foregoing description it will be readily seen that the acceleration-curve will be somewhat jagged by reason of the slight rising of the current above the normal accelerating-current and then gradually falling slightly below the normal accelerating-current but by introducing asufficient number of resistances with a corresponding increase in the number of the cooperating contacts and contact-strips this acceleration may be made practically constant, thereby developing sub stantially the straight acceleration-curve C until the position indicated by line B is attained, when the movement effected by the motorman of the controller to the position indicated by line 0 effects a cutting in of more coils into the motor-field circuit, thereby arresting the acceleration and hence producing the straight horizontal line E, Fig. 8, in the aceeleration-curve, which indicates the uniform speed thereafter.

When it is desired to stop the train, the controller-lever is moved by the motornian, thereby moving the controller-cylinder to the position indicated by dotted line D, Fig. 1, which is the off position, thereby breaking all the motor-circuits, and the application of the brakes thereupon brings the train to a stop.

In Fig. 2 I have shown in diagram the circuits corresponding to the several positions A B O of the controller-cylinder, and from this diagram it will be seen that in position A the motor operates with a portion of the field-coils cut out of circuit or short-circuited and with all the resistances included in circuit. In the position B all the resistances are cut out and the motor operates with a portion of the field-coils short-circuited, and in the position 0, which is the last position before the off position is attained, and which position corresponds to the uniform speed which is maintained after the desired degree of acceleration has been developed, the motor operates with all its field-coils in circuit and with no resistance.

From the foregoing description it will be seen that the acceleration of the motor in starting may be effected in two ways-viz., by varying the resistance included in the circuit, and, secondly, by varying the coils of the motor-fieldthe cutting out of the resistances of the motor-circuit serving to increase the current through the motor and hence to counteract the development of counter electromotive force in the motor-armature. In

the other case the cutting in of coils in the motor-field increases the number of magnetic lines of force out by the motor-armature and hence builds up the counter electromotive force of the armature, thereby reducing its acceleration.

In Fig. 3 I have shown diagrammatically a slightly-modified arrangement wherein both of these methods of varying the acceleration are employed. In this arrangement I employ a comparatively small amount of resistance, all of the field-magnet coils being included in the motor-circuit at the time of starting, and hence a large number of lines of force are urged through the magnetic circuit of the motor, and in this arrangement I use a portion of the counter electromotive force of the motor to maintain a uniform current during acceleration, instead of some of the resistances, as described in connection with Fig. 1. In this arrangement and method when the controller is first moved to position A, which is the initial movement of the controller by the motor-man, the current traverses the following path: from trolley T, through all the windings of the motor field coils, through motor M, resistances R R R, contact 5, strip 5, to strip 9*, contact 9, connection a, auxiliary motor I connection I), relay Q, and connection gto ground. The motor thereupon starts up and begins to accelerate rapidly, as indicated in the diagram Fig. 4, in the position A, all the resistances being in circuit and all the coils of the fieldmagnet being also included in circuit. Through the automatic action of relay Q and auxiliary motor K, as above explained,'the controller-cylinder is advanced to the posi tion indicated at A Fig. 3, thereby bringing strip 6 into contact with contact 6, thus cutting out resistance R, and thereupon the motor operates as indicated at N, Fig. 4:, with only resistances R and R in circuit and with the same conditions above described of the field-coils until the current again falls below the normal accelerating-point, thereby again elfecting an action of the automatic mechanism to advance the controller to the position indicated by line A Fig. 3, thereby cutting out resistance R as indicated at line A Fig.

at, the circuit condition being the operation of the motor with only resistance R in circuit and with the same condition of fieldwindings as before. Thus finally the controller arrives at the position 13, at which point all the resistances are cut out, as indicated at line B, Fig. 4, and simultaneously therewith the strips 1 and 2 make electrical connection with points 1 and 2, thereby shortcircuitin g one of the coils of the motor-field. This increases the accelerating-current of the motor by reducing the number of lines of magnetic force which are forced through the armature, and hence maintains the constant acceleration until the counter electromotive force developed in the armature reduces the current to a point where the automatic mechanism above described again comes into play and moves the controller-cylinder to the position B This position brings the strip 3 into contact with point 3, thereby cutting out anothercoil or coils of the motor-field, as indicated at line B Fig.4, and consequently again increasing to a point slightly above the normal the accelerating-current until such current again falls by the development of counter electromotive force, thereby effecting an other actuation of the automatic auxiliary motor and relay, and hence advancing the controller to the position B and hence bringing strip 4 into contact with point 4, thereby cutting out another or other coils of the motor-field, and hence a repetition of the above action. At this point in the operation the controller is brought to a position where, if the parts are left without further movement, a too great a speed would be developed. Therefore a furthur movement of the controller to uniformspeed position, as indicated by dotted line C, is efifected by the motorman, thereby breaking contact between strips 1, 2*, 3, and 4;

and their corresponding contacts 1 2 3 4t, and hence again cutting into the motor-circuit all of the field-coils, thus increasing the lines of forcein the magnetic circuit of the motor, and hence building up the counter electromotive force of the motor and reducing its speed to a uniform point, thereafter operating the motor with all its field-coils in circuit and with no resistance.

The several positions A A A and 13/13 13 represent the several steps in the operation for efiecting the constant acceleration, and when the desired speed has been attained position 0 indicates the continuation of the motor to operate at that constant speed, and when it is desired to stop the car the motorman moves the controller to the position D, or off position, thereby breaking the circuits of the motor, whereupon an application of the brakes effects a stopping of the car.

I other step to the position A.

ing the electrical connections above described In the foregoing description I have described my invention as applied to single-motor equipments; but it is obvious that the principles thereof are equally well adapted for use in connection with two or more motors placed on each axle of the car.

In Fig. 5 I have shown an adaptation of my invention for producing a constant acceleration-current until the desired degree of speed has been attained, and thereafter a constant speed, in connection with two or more motors, and embodying the change from series to series parallel or to parallel relation of the 1110- tors. In this arrangement I divide the controller-cylinder into five parts D, D D, D, and D insulated from each other and each part containing electrically-connected contact-strips, and I provide cooperating contacts 1 2 3, &c., forming the terminals of the fieldwindings of the several motors employed and also the terminals of the circuits which include the resistances R R. Then it is desired to start the motors from rest, the motorman turns the controller to the position indicated by line A, thereby completing circuit through points 8, 9, 14, and 15 and their cooperating strips 8, 9, 14 and 15, and thereupon the circuit is completed from the trolley T, through motor M, the windings F of the fieldmagnet of motor M, to contact 9, strip 9", strip 8, contact 8, motor M all the windings F of the field of motor M through resistances R R, to contact 14, strip lit, to 15, to contact 15 and connection a, and thence on through the automatic arrangement above described in connection with Figs. 1 and 3. Thus, as indicated at A, Fig. 6, the motors are started, the arrangement of the motors being in series and including all the resistances R R and all the coils of the field-magnets of all the motors, and the acceleration of the motors begins. WVhen the accelerating-current begins to fall by reason of the counter electromotive force developed,the controller-cylinder is advanced a step by the action of the automatic arrangement, as above explained, to position A thereby bringing strip 13 into contact with point 13 and hence cutting out resistance R, as indicated in diagram at A Fig. 6. This restores the accelerating-current to a point slightly above the normal until further development of counter electromotive force in the motors again reduces the acceleratingcurrent to a point such as to bring into action the automatic mechanism above explained, which advances the controller-cylinder another step and to position A causing strip 12 to contact with point 12, thus cutting out all the resistance, as indicated at A Fig. 6, and hence again restoring the acceleratingcurrent to a point slightly above the normal. Further reduction of such current again causes the controller-cylinder to advance anlVithout alterthis advancement of the controller-cylinder brings contact-strips 1 2 and t 5 into contact with their corresponding points 1 2 and- 4 5, thereby short-circuiting a portion of the field-windin gs of both motors, as indicated in diagram at A, Fig. 6. This reduction of the ampere-turns of the motor-field windings serves to restore the accelerating-current by reducing the lines of force in the magnetic circuits of the .motors. This condition is maintained until the acceleratingcurrent again falls slightly below the normal, whereupon the controller-cylinder is advanced automatically to the position A thereby bringing strips 3 and 6", respectively, into contact with points 3 and 6, thus again cutting out additional coils in the field-windings of the motors, and hence correspondingly increasing the accelerating-current by still further reducing the lines of force in the magnetic circuits of the motors. Upon a fall of theaccelerating-current to a point slightly below the normal the controller-cylinder is ad-' vanced again automatically to the position A, which is a step necessary preparatory to a change of the relation of the motors from series to series parallel or to parallel. At this point it is necessary to operate the controller by hand, inasmuch as the acceleratingcurrent has not been increased by the last automatic action, but rather has been still further decreased by cutting in more turns of the motor-field windings. Therefore at this point the motorman actuates the controller to-advance it to the point A This movement brings contacts 10 11 into contact with points 10 and 11, respectively, and hence changes the connections of the motors in the particular arrangement illustrated from se ries relation to parallel relation, as indicated at A Fig. 6. During this step or transition from series to parallel it is desirable to again interpose resistance. I therefore provide a gap in strip 12. If desi.red,only one of the motors may be employed during this transition step, and hence a similar gap may be provided in strip 8. In a similar manner, if desired, gaps may also be provided in strips 3 and 6 However, whatever the changes may be during this movement or change at the end thereof, the motors operate, as indicated at A in parallel, with only a portion of the field-windings of each short-circuited. This transition serves to increase the accelerating-current to a point slightly above the normal, and hence the automatic mechanism is again brought into play when such current falls below the normal to advance the controller to the point A thereby through suitable connections, as shown, cutting out more coils of the fieldwindings of one or both motors, but leaving the motors in parallel, and hence again increasing the accelerating-current, and so on, until finally the desired acceleration has been attained. When in position A", all the fieldwindings are again out into live circuit, thereby arresting the acceleration and reducing the current to the point necessary to maintain a constant speed, and, finally, when it is desired to stop the car the motorman turns the controller to the position D, or to the off position, thereby breaking all the circuits, when, upon application of the brakes, the cars will stop as desired.

I do not desire to limit myself to the use of only two motors, as it is evident that any number of motors may be employed in association with the method of control embodying the principles above set forth. If four or more motors are used, which may be placed, respectively, in series, series parallel, and, finally, in parallel, and in making the changes from one to the other, the contact-strips and cooperating contact-points of the controller may be so relatively adjusted and arranged as to cut out more or less of the windings of the field of one or several of the motors and to cut into circuit a desirable resistance to produce a uniform acceleration and a uniform current in each motor until the desired speed has been attained, and thereupon the windings of the field-magnets of all the motors may again be replaced in circuitin order to reduce the current to a point where it will operate the motors to propel the train at a uniform speed.

In the operation of a controlling method embodying my invention it will be obvious from the foregoing description that the power developed increases constantly and uniformly coincident with the constant acceleration of speed up to the point where the acceleration is arrested. At this point, however, a greater power is being developed than is required to continue to operate the motor at a uniform speed. Therefore the action of reducing the current to a point such as to maintain a uniform speed, after the desired speed has been attained, also causes the power to drop to a point just necessary to carry the train at the required uniform speed. In the diagram Fig. 9 I have shown the powercurve illustrating this operation, 0 designating the development of power during the constant acceleration, C indicating the fall of power when the desired speed has been attained, and 0 indicating the constant power applied thereafter to maintain the uniform speed. I

It is evident that the principles of my invention may be embodied in a wide variety of specific forms of apparatus. I do not desire, therefore, to be limited or restricted to the specific details and arrangements shown and described, and while I have shown and described as embodiments of the generic conception of my invention specific forms wherein the results sought are attained by varying the field-windings of the motors and also by varying the relative connections of two or more motors I do not claim the same specifically herein, as the subjects-matter thereof are covered in divisional applications,Serial Nos. 655,911 and 655,912, filed October 21, 1897; but,

Having now set forth the obj ect and nature of my invention and a form of apparatus embodying the principles and mode of operation thereof, what I claim as new and useful and of my own invention, and desire to secure by Letters Patent of the United States, is

1. The method of controlling motors which consists in maintaining a substantially constant or uniform accelerating-current until the desired speed has been attained,and thereafter reducing said current thereby maintaining a uniform speed, as and for the purpose set forth.

2. The method of controlling motors which consists in varying the resistance of the motor-circuit to maintain a substantially uniform accelerating-current, and finally reducing the motor-current to produce uniform speed, as and for the purpose set forth.

3. The method of controlling motors which consists in varying the resistance and also the field-windings in the circuit of two or more motors and then varying the relative connections of said motors, to maintain a substantially uniform acceleratingcurrent, and finally reducing the motor-current to a point such as to maintain a constant speed, as and for the purpose set forth.

at. The method of controlling motors which consists in varying the resistance and also the field-windings in the motor-circuit to maintain a substantially uniform accelerating-current, and thereafter reducing the motor-current to a point such as to maintain a constant speed, as and for the purpose set forth.

5. The method of controlling motors which consists in gradually cutting out resistance and also the field-windings in the motor-circuit to maintain a substantially uniform accelerating-current, and finally restoring the field-coils to the motor-circuit whereby acceleration is arrested, the operating-current reduced, and the motor is maintained at a uniform speed, as and for the purpose set forth.

6. The method of controlling motors which consists in gradually cutting out resistance from the motor-circuit as the motor attains its speed, in order to produce a substantially uniform accelerating-current, and finally increasing the strength of the motor-field there by reducing the current to a point such as to maintain a uniform speed, as and for the purpose set forth.

said contacts for maintaining a substantially uniform accelerating-current until the desired speed has been attained, and means also controlled by said contacts for thereafter reducing the current to a point such as to maintain a uniform speed, as and for the purpose set forth.

10. The combination with a motor circuit therefor and resistances initially included in said circuit, of means for successively cutting out said resistances as the motor starts up, whereby a substantially uniform current is maintained until the desired speed is attained, and means for finally arresting the acceleration and reducing the current to a point such as to maintain a uniform speed, as and for the purpose set forth.

. 11. The combination with a motor circuit therefor, resistances and field-coils initially included in said circuit, means actuated by the fall of current due to the development of counter electromotive force for gradually removing said resistance and field-coils from said circuit, and means for finally restoring said field-coils to said circuit, as and for the purpose set forth.

12. In a motor-controller, relatively movable and stationary contacts, motor-circuits controlled thereby, means for automatically moving said movable contacts to vary the motor connections, whereby a substantially uniform accelerating-current is maintained until the desired speed is attained, in combination with means for finally reducing the current to a point such as to maintain the motor at uniform speed, as and for the purpose set forth.

13. In a motorcontroller resistances arranged in the motor-circuit, means actuated by the fall of accelerating-current due to the development of counter electromotive force in the motor, for gradually cutting out said resistances, thereby maintaining a substantially uniform accelerating current, and means for finally reducing the current to a point such as to operate the motor at uniform speed, as and for the purpose set forth.

14. In an apparatus of the class described, a motor, a circuit therefor, resistances and field-coils initially included in said circuit, relatively stationary and movable contacts arranged to gradually remove said resistances and coils from, said circuit, an auxiliary motor arranged in said circuit and actuated by fall of current due to the development of counter electromotive force,as the motor starts up, and means actuated by said auxiliary motor for moving said movable contacts, said contacts arranged to restore said field-coils to working circuit when the desired speed is attained, as and for the purpose set forth.

15. The combination with two or more motors, a circuit therefor, resistances and motorfield coils initiallyincluded in series with said motors, relatively stationary and movable contacts arranged when relatively moved to gradually remove said resistances and coils from said circuit and to vary the relative c011- nections of said motors, said contacts adapted to finally restore said coils to working circuit, and means actuated by fall of current due to the development of counter electromotive force, as the motor starts up, for moving said movable contacts, as and for the purpose set forth.

16. In an apparatus of the class described, a controller-cylinder, contacts carried thereby, for varying the motor-circuits, an auxiliary motor arranged in circuit with the main motor, and adapted to be actuated by the rise and fall of current due to variations in the motor-circuits and the development of counter electromotive force, said auxiliary motor arranged to actuate said controller-cylinder, as and for the purpose set forth.

17. In a motor-controller, a motor-circuit therefor, relatively movable and stationary contacts means controlled by said contacts for maintaining in said circuit a substantially uniform accelerating-current until the desired speed is attained, and means also controlled by said contacts forthereafter reducing the current to a point such as to maintain a uniform speed, an auxiliary motor arranged in said circuit and actuated by fall of current due to the development of counter electromotive force, as the motor starts up, and means actuated by said auxiliary motor for moving said movable contacts, as and for the purpose set forth.

18. The combination With a motor, a circuit therefor, relatively movable and stationary contacts, means controlled by said contacts for maintaining in said eircuita substantially uniform acceleratingcurrent until the desired speed has been attained,means also controlled by said contacts for thereafter reducing the current to a point such as to maintain a constant motor speed, an auxiliary motor arranged in said circuit, a relay actuated by' 

